Hi endomtrial cells are shed during period..so that could well be the cause of it, there are other possibilities also such a hpv which is why your Dr is wise in getting a biopsy.....odds are its from your cycle but sure best to err on the side of caution,
I know it is easy for someone to say try not to worry, but please try not to too much , let me know when you get the biopsy how it goes ok,,and you may as well schedule it asap so you can get the results and then not have to worry.
I just read your private message to me. In July 2008 I had normal endometrial cells show up on my pap test too when I was 43. My then gynecologist said she was required to do an endometrial biopsy because I was over 40.But because I have read *SO MANY COUNTLESS* women say on this site and countless others how painful the regular endometrial biopsy is,I contacted the company Gynecor that makes the TruTest Tao brush biopsy test,and I asked for a sales rep in my area and she emailed me back and gave me local doctors names who use this test.I had it done in September 2008,and it came back benign.My period had just ended two days before and my former gynecologist and studies I've read say this can be one of the causes for this and it's more common than some people think.It's not very common,but it's not rare to happen either.
Actress Fran Drescher was misdiagnosed with endometrial cancer by *8* different doctors for 2 years who thought her spotting in between her period was just from being premenopausal,and at 42 she finally had a biopsy and she had a uterine tumor the size of a walnut by then! That was ten years ago and she's in great health now.She has written and spoken a lot and tried to get laws passed for better tests for better early detection for gynecological cancers and she supports the TruTest biopsy.